JPS6212192B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing carbon material used for blade materials of dry pumps, and more specifically, the present invention relates to a method for manufacturing carbon material used for blade materials of dry pumps. The present invention relates to a method for producing a carbon material that improves sliding noise and abrasion resistance by incorporating expanded graphite, which has excellent properties. Carbon materials are used as blade materials for dry pumps because they are self-lubricating without the need for oil. However, when conventional carbon materials are used as blade materials, sliding noise and wear are large. As a means to improve this, methods include changing the type of aggregate used in carbon materials and adding solid lubricants to the aggregate, but since the magnitude of sliding noise and the magnitude of wear are contradictory, However, these means have the disadvantage that if the sliding noise is reduced, the wear will increase, and conversely, if the wear is reduced, the sliding noise will become large. For example, sliding noise can be reduced by lowering the elastic modulus of the carbon material, but if the elastic modulus of the carbon material is lowered using conventional methods, the mechanical strength will decrease and wear will increase. As a result of various studies, the present inventors have found that it is extremely effective to blend expanded graphite into the aggregate used for carbon materials as a means to improve the above-mentioned sliding noise and wear characteristics. The present invention involves blending 50% by weight or more of aggregate used in carbon materials and 50% by weight or less of expanded graphite, further adding a binder to the mixture, and then kneading, crushing, molding, and sintering the carbon materials. Regarding the manufacturing method. The aggregate used in the present invention includes ordinary natural graphite (for example, scale graphite, earthy graphite, etc.),
Artificial graphite, calcined coke, or a mixture thereof is used, and the binder is tar, pitch, synthetic resin, etc. Expanded graphite is obtained by a normal method. For example, natural scale graphite is treated with a mixed acid of concentrated sulfuric acid and concentrated nitric acid, and then washed with water.
By dehydrating and expanding at 800°C to 1200°C, expanded graphite is used that has expanded to 10 to 200 times the volume of the raw graphite. As graphite, natural scaly graphite, earthy graphite, etc. can be used, as well as artificial graphite. Systems for treating graphite with acids include fuming nitric acid, concentrated sulfuric acid-potassium permanganate, concentrated sulfuric acid-potassium chlorate, Concentrated sulfuric acid-potassium dichromate, etc. can be used. Further, it is desirable that the shape of the expanded graphite is approximately the same as the particle size of the aggregate used, taking into account the effects of improving miscibility and sliding properties. As the blending ratio of expanded graphite increases, the elastic modulus decreases as shown in FIG. 1, and the sliding noise accordingly decreases as shown in FIG. 2. The effect begins to appear when expanded graphite is added. However, as shown in Figure 3, the wear rate ratio decreases in proportion to the proportion of expanded graphite up to 30% by weight, reaches a minimum value at 30% by weight, and then increases when it exceeds 30% by weight. Furthermore, when it exceeds 50% by weight, it becomes rapidly larger than conventional carbon materials. Therefore, the mixing ratio that improves both sliding noise and wear characteristics is 50% by weight of aggregate.
Up to 50% by weight of expanded graphite is added to the above. In the present invention, the blending amount of expanded graphite and the blending amount of the binder are shown below. Expanded graphite content = Expanded graphite weight / Aggregate weight + Expanded graphite weight x 100 Binder content = Binder weight / Aggregate weight + Expanded graphite weight x 100 The carbon material of the present invention is used for general carbon materials. In addition to the aggregate, expanded graphite, and binder, an appropriate amount of solid lubricant such as molybdenum disulfide or graphite fluoride is added as required and kneaded, and then crushed and molded using conventional methods. Obtained by firing in a kiln at a temperature of 800-1200°C. The present invention will be explained with reference to Examples below.Example 1 70% by weight of artificial graphite with an average particle size of 40 microns and expanded graphite with an average particle size of 50 microns (manufactured by Hitachi Chemical Co., Ltd.)
56% by weight of coal tar pitch (softening point: 85°C) was added to a 30% by weight mixture (trade name: HGP), and the mixture was heated and kneaded at 220°C for 1 hour in a kneader. This kneaded material was pulverized, pressed, and fired in a conventional manner to obtain a carbon material. Example 2 60% by weight of artificial graphite with an average particle size of 40 microns, 20% by weight of natural scale graphite with an average particle size of 20 microns, and expanded graphite with an average particle size of 50 microns (Hitachi Chemical Co., Ltd.)
A carbon material was obtained in the same manner as in Example 1 by adding 49% by weight of coal tar pitch to a 20% by weight mixture (manufactured by HGP (trade name: HGP)). Next, regarding the carbon materials obtained in Example 1 and Example 2, a vacuum dry pump manufactured by Orion Kikai Co., Ltd.
The test was conducted using KRA-8 model. The results are shown in Table 1. Table 1 also shows test results for carbon materials conventionally used as blade materials as comparative examples. The test conditions at that time were as follows. 1 Ultimate vacuum: 400mmHg 2 Rotation speed: 1240 rotations (rpm) 3 Sample dimensions: 51 (mm) x 162 (mm) x height 6.9
(mm) 4 Atmosphere: Room temperature in air 5 Test time: 300 hours

[Table] As is clear from the above examples, if a carbon material made by blending expanded graphite with the aggregate used in general carbon materials is used as a blade material, the sliding noise and wear resistance will be significantly improved. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between expanded graphite blending ratio and elastic modulus, Figure 2 is a graph showing the relationship between expanded graphite blending ratio and sliding noise, and Figure 3 is a graph showing the relationship between expanded graphite blending ratio and wear rate ratio. This is a graph showing.

Claims (1)

[Claims] 1. A method for producing a carbon material, which comprises blending 50% by weight or more of aggregate and 50% by weight or less of expanded graphite, further adding a binder to the blend, and then kneading, crushing, molding, and firing.